Comparative effectiveness of ChAdOx1 versus BNT162b2 covid-19 vaccines in health and social care workers in England: cohort study using OpenSAFELY
Authors: William J Hulme, Elizabeth J Williamson, Amelia C A Green, Krishnan Bhaskaran, Helen I McDonald, Christopher T Rentsch, Anna Schultze, John Tazare, Helen J Curtis, Alex J Walker, Laurie A Tomlinson, Tom Palmer, Elsie M F Horne, Brian MacKenna, Caroline E Morton, Amir Mehrkar, Jessica Morley, Louis Fisher, Sebastian C J Bacon, David Evans, Peter Inglesby, George Hickman, Simon Davy, Tom Ward, Richard Croker, Rosalind M Eggo, Angel Y S Wong, Rohini Mathur, Kevin Wing, Harriet Forbes, Daniel J Grint, Ian J Douglas, Stephen J W Evans, Liam Smeeth, Chris Bates, Jonathan Cockburn, John Parry, Frank Hester, Sam Harper, Jonathan A C Sterne, Miguel A Hernán, Ben Goldacre
Journal: BMJ (2022)

Abstract Objective To compare the effectiveness of the BNT162b2 mRNA (Pfizer-BioNTech) and the ChAdOx1 (Oxford-AstraZeneca) covid-19 vaccines against infection and covid-19 disease in health and social care workers. Design Cohort study, emulating a comparative effectiveness trial, on behalf of NHS England. Setting Linked primary care, hospital, and covid-19 surveillance records available within the OpenSAFELY-TPP research platform, covering a period when the SARS-CoV-2 Alpha variant was dominant. Participants 317 341 health and social care workers vaccinated between 4 January and 28 February 2021, registered with a general practice using the TPP SystmOne clinical information system in England, and not clinically extremely vulnerable. Interventions Vaccination with either BNT162b2 or ChAdOx1 administered as part of the national covid-19 vaccine roll-out. Main outcome measures Recorded SARS-CoV-2 positive test, or covid-19 related attendance at an accident and emergency (A&amp;E) department or hospital admission occurring within 20 weeks of receipt of the first vaccine dose. Results Over the duration of 118 771 person-years of follow-up there were 6962 positive SARS-CoV-2 tests, 282 covid-19 related A&amp;E attendances, and 166 covid-19 related hospital admissions. The cumulative incidence of each outcome was similar for both vaccines during the first 20 weeks after vaccination. The cumulative incidence of recorded SARS-CoV-2 infection 20 weeks after first-dose vaccination with BNT162b2 was 21.7 per 1000 people (95% confidence interval 20.9 to 22.4) and with ChAdOx1 was 23.7 (21.8 to 25.6), representing a difference of 2.04 per 1000 people (0.04 to 4.04). The difference in the cumulative incidence per 1000 people of covid-19 related A&amp;E attendance at 20 weeks was 0.06 per 1000 people (95% CI −0.31 to 0.43). For covid-19 related hospital admission, this difference was 0.11 per 1000 people (−0.22 to 0.44). Conclusions In this cohort of healthcare workers where we would not anticipate vaccine type to be related to health status, we found no substantial differences in the incidence of SARS-CoV-2 infection or covid-19 disease up to 20 weeks after vaccination. Incidence dropped sharply at 3-4 weeks after vaccination, and there were few covid-19 related hospital attendance and admission events after this period. This is in line with expected onset of vaccine induced immunity and suggests strong protection against Alpha variant covid-19 disease for both vaccines in this relatively young and healthy population of healthcare workers.